Simulation study of tertiary current distributions on rotating electrodes

Abstract

The tertiary current distributions on rotating electrodes have been studied by using the numerical simulation method. An acid copper sulphate electrolyte composed of 0·3M CuSO₄ and 1·9M H₂SO₄ was used within an electrochemical cell of practical dimensions. The rotating disc had a diameter of 6 mm, within which the working electrode with diameter of 3 mm was located at the bottom centre of the disc. The distributions of ion concentrations were obtained by two-dimensional fluid flow simulation and the solution of mass transport equations based on axial symmetry. The calculated concentration boundary layer thicknesses agree well with those obtained from the Levich equation. It is found that the tertiary current distribution on the working electrode is affected by the rotating velocity of the electrode, even if currents are considerably below the limiting current. The effect disappears with the increase in rotating velocity up to 1000 rev min⁻¹ in comparison with the secondary current distribution. The tertiary current distributions for three types of working electrode have been calculated and an improved shape of working electrode is proposed. Since the working electrode is normally used for electrochemical measurements, e.g. polarisation characteristics, which are applied for the calculation of current distribution in the present work, the present study would provide beneficial results to improve the accuracy of measurements.